Organized activity participation provides opportunities for adolescents to develop assets that may support favorable outcomes in young adulthood. Activity participation may be especially beneficial for marginalized youth because they are likely to face stressors that increase risk of negative outcomes. We used growth mixture modeling to identify activity participation trajectories among African American adolescents in an urban, disadvantaged community (Wave 1: mean age = 14.86 years, standard deviation = 0.64; 49% male, N = 681). We also investigated if young adult outcomes differed by participation trajectory subgroups, the results of which suggested that a 3‐class model best fit the data: low initial and decreasing levels of participation (74%); moderate initial and consistent (21%); and moderate initial and increasing (5%). Adolescents in the increasing class reported higher life satisfaction and lower substance use in young adulthood compared to the decreasing class. Youth who increase participation in activities over time may experience greater opportunities for building assets related to positive development that support health and well‐being into young adulthood.